In the injection molding process for plastic products, the amount of water contained in raw materials is generally required not to exceed 5%. As a result, drying and conditioning need to be performed on the raw materials before the injection molding process, and the general process for drying and conditioning treatment is performed on the raw materials at a temperature of 90-200° C. for 1-6 hours.
Conventionally, the injection molding hopper is provided with a special conditioning and drying device before a thermostatic bucket, the raw materials are then further sent into the thermostatic bucket after the drying and conditioning are completed, and a large amount of heat is dissipated during the process. Additionally, the existing conveying process could easily cause secondary pollution of the raw materials; therefore, not only is it a waste of human and material resources, but it also greatly affects the quality of products.
In addition, during the injection molding process of multi-layer composite plastic products, as the drying and conditioning processes of the different raw materials adopt different temperatures and times, a plurality of special conditioning and drying devices are required for processing a variety of the different raw materials, which make the above-mentioned problems become particularly worse.
The Chinese patent (Publication No. CN101491935A, published on Jul. 29, 2009) discloses a system and a method for synchronously controlling temperature of a hopper of an injection molding machine, and aims at providing the system for enabling the temperatures of all sections of the hopper in the injection molding machine to be synchronous and a control method thereof. The system comprises a plurality of electric heaters positioned in the positions of all the sections of the hopper and temperature sensors in the corresponding mounting positions. All the temperature sensors are connected to a temperature setting module through signal wires. The temperature setting module, a temperature synchronization control module and a PID (proportion integration differentiation) control module are sequentially connected through the signal wires. The PID control module is connected to all the electric heaters through the signal wires.
Under the situation that the temperatures of all the sections of the hopper of the injection molding machine are set to be inconsistent or the heat radiation situations are inconsistent, the temperatures of all the sections can simultaneously achieve the set value by rapid control. When errors between the temperature set value and the actual values of all the sections of the hopper are detected in a real-time manner, control outputs of all the sections are obtained for controlling all the sections of the heaters to work, thereby realizing precision control of the temperatures of all the sections and achieving the effects of enabling the temperatures of all the sections of the hopper of the injection molding machine, so as to make the temperatures of all the sections of the hopper synchronous and rapidly achieve the set temperature.
The method of the Chinese patent (Publication No. CN101491935A) provides the sectional temperature control assumption for the single hopper, which is conductive to improve the temperature control precision. However, the method cannot solve the following technical problems: (1) the amount of energy consumption in the link of transferring the raw materials in the injection molding process is significant, (2) the labor intensity of workers is high, (3) secondary pollution of the raw materials occurs frequently, and (4) decreased product quality.